A continuously variable transmission (hereinafter referred to as a “CVT”) continuously changes a speed ratio by changing widths of grooves in a primary pulley and a secondary pulley around which a belt is wound. Torque transmittable by the CVT is determined by a force by which the primary pulley and the secondary pulley thrust the belt (hereinafter referred to as a “pulley thrust force”), and the pulley thrust force is determined by a primary pressure and a secondary pressure supplied to the primary pulley and the secondary pulley.
Therefore, the CVT makes transmittable an input torque to the CVT determined by an engine torque and a torque converter torque ratio, without slippage of the belt, by controlling the primary pressure and the secondary pressure such that the transmittable torque does not become smaller than the input torque.
Furthermore, if an input rotation speed of the CVT changes, an inertia torque is input to the CVT, and torque that the CVT actually needs to transmit increases or decreases accordingly. Therefore, the transmittable torque can be ensured, without excess or deficiency, by calculating the inertia torque input to the CVT and correcting the primary pressure and the secondary pressure in accordance with the calculated inertia torque.
It should be noted that JP 11-20512A describes an inertia torque input to a CVT and a method for calculating the same.